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A One Billion Year Lap

Although the number of galaxies is so vast that they cannot be accurately counted, they have one thing in common. All disk galaxies, no matter their size or mass, rotate once every billion years.

“It’s not Swiss watch precision,” said Gerhardt Meurer, an astronomer from the International Centre for Radio Astronomy Research (ICRAR), “but regardless of whether a galaxy is very big or very small, if you could sit on the extreme edge of its disk as it spins, it would take you about a billion years to go all the way round.”

The finding was published March 9, 2018, by the Royal Astronomical Society. In reaching this conclusion, astronomers measured the radial velocities of a number of galaxies, varying in size and rotational velocities by up to a factor of 30. In every case, the total time for an object on the outer edge of the galaxy to make a complete loop came in at close to one billion years.